The present invention relates to a local communication system comprising a plurality of stations interconnected in a network for the communication of messages, and in particular, to the behaviour of the system upon failure of start-up. The invention further relates to stations for use in such a system, and methods of operation therein.
A local communication system which combines source data (CD audio, MPEG video, telephone audio etc) with control messages in a low cost fibre network has been proposed in the form of D2B Optical. For details, see for example the xe2x80x9cConan Technology Brochurexe2x80x9d and the xe2x80x9cConan IC Data Sheetxe2x80x9d available from Communication and Control Electronics Limited, 2 Occam Court, Occam Road, The Surrey Research Park, Guildford, Surrey, GU2 SYQ, United Kingdom (also http://www.candc.co.uk). See also Eurpoean patent applications of Becker GmbH EP-A-0725516 (95P03), EP-A-0725518 (95P04), EP-A-07225515 (95P05), EP-A-0725520 (95P06), EP-A-0725521 (95P07), EP-A-0725522 (95P08), EP-A-0725517 (95P09) and EP-A-0725519 (95P10). xe2x80x9cConanxe2x80x9d is a registered trade mark of Communication and Control Electronics Limited. xe2x80x9cD2Bxe2x80x9d is a registered trade mark of Philips Electronics NV.
A problem recognised with any form of communication system is the problem of locating a fault in the network. Many new expensive local area networks comprise bidirectional (dual fibre) links, such that a break at one point does not prevent communication and fault diagnosis in unaffected parts of the network. In a ring network of the type described, made of unidirectional links, such as D2B Optical, however if there is a break in the network at any point, the master station will simply fail to achieve synchronisation, but the location of the fault is not indicated.
To address this problem in a computer network, comprising unidirectional links U.S. Pat. No. 3,564,145 and EP-A-0035789 are proposed mechanisms in which a station immediately following the fault location in the ring can adopt a temporary master status, in order to communicate the fault position to another station. In particular, the temporary master station communicates its unit network address to the master station, where it can be used, to assist in fault diagnosis.
Each of these known mechanism relies on the fact that each station has a unique address or other identifier in the known D2B Optical network, each station can be addressed by ring position or by a function-related device address, as described in our copending application PCT/GB98/00872 (62792WO). However, on start-up, stations are not yet aware of their ring position and their device addresses may not yet have been assigned. Accordingly, the known mechanisms are unable to provide an indication of the fault location for diagnostic purposes in such a system.
The invention provides a local communication system comprising a plurality of stations, in which one station is designated a master station and the other stations designated as slave stations, the plurality of stations being interconnected by point-to-point links in a ring network for the exchange of data messages, wherein each station is arranged, in a start-up procedure, to recognise a signal received from a preceding station in the ring and to transmit a corresponding signal to a following station in the ring, and wherein, in the event that recognition is not obtained within a predetermined time, a start fault procedure is implemented, the start fault procedure implemented by each station comprising:
configuring each slave station to act as temporary system master, generating its own output signal for recognition by the following station in the ring;
in the event that recognition of a signal from the preceding station in the ring is still not achieved, generating a message indicating a default ring position;
in the event that recognition of a signal from the preceding station is obtained, reverting to slave status, receiving said message and transmitting to the following station a modified message so as to indicate an incremented ring position; recording in at least one designated diagnostic station, an indication of the ring position indicated by a message received by the designated diagnostic station, as an indication of fault position for diagnostic purposes.
The ring position may be recorded for diagnostic purposes by the master station.
In the event that recognition is achieved by all stations around the ring (normal start-up), the same message indicating a default ring position may be generated by the master station, and modified by each slave station to determine that slave station""s own ring position. After transmission and modification of said message around the ring, each station may be responsive to messages addressed to it individually by reference to said ring position. Each station may be further responsive to messages addressed to it individually by reference to a logical address. The start-up may be initiated by a signal distributed independently of said point-to-point links.
The network may convey digital audio data together with control messages in a regular frame structure. The stations may generate said signals in synchronism.
The invention further provides apparatus for use as the slave and master stations in a system according to the inventions set forth above.
The invention further provides methods of operation, as set forth above.